Planning stages: Vienna to Croatia to Prague?

Hey Guys,
I am looking for suggestions for places to ride and hire a bike for an upcoming trip this summer. I have purchased a ticket to Vienna with almost zero commitments and almost no plans as of now. I will be going for 19 days from the first week of May to the last and I would like to spend a solid portion of that on a bike. As of now, I am looking into Prague for a beer festival (this is an MTB forum afterall), and possibly down to Slovenia and Croatia. As for transportation I will be relying on public transit and the possible generosity of other mountain bikers, but I will have limited to no access to a vehicle.

So my real question to you all is this:

I have a plane ticket to Vienna, a pack of riding gear, a month, and zero plans, what would you do?